1. Field of the Invention
The present invention relates to a torque variation absorbing device to be mounted in a torque transmission path of an automobile, an industrial vehicle, and a ship, etc.
2. Description of the Related Art
FIG. 7, identified as Prior Art illustrates a conventional torque variation absorbing device disclosed in Japanese Utility Model Publication SHO 61-23545. As illustrated in FIG. 7, the torque variation absorbing device includes a drive side flywheel 150, a driven side flywheel 151, a torque limiting mechanism 152, a spring mechanism 153 (a damping mechanism), and a hysteresis mechanism 154. The torque limiting mechanism 152, the spring mechanism 153 and the hysteresis mechanism 154 are disposed between the drive side flywheel 150 and the driven side flywheel 151. A bearing 155 is installed between the drive side flywheel 150 and the driven side flywheel 151 so that the drive side flywheel 150 and the driven side flywheel 151 are rotatable relative to each other about a common rotational axis.
FIG. 8, identified Prior Art illustrates the structure of the ball bearing 155 more in detail. As illustrated in FIG. 8, the ball bearing 155 includes an outer race 156, an inner race 157, a plurality of balls 158, and a retainer 159. The balls 158 are equally spaced from each other in a space defined between the outer race 156 and the inner race 157 and are held by the retainer 159 so that the distance between two adjacents balls are maintained constant. This type of ball bearing where a gap is provided between any two adjacent balls is called a deep groove ball bearing.
FIG. 5, identified as Prior Art illustrates how to assemble a usual deep groove ball bearing. In the assembly, firstly, a center of an inner race 101 is offset from a center of an outer race 100 so that a space having the shape of a crescent 102 is formed between the outer race 100 and the inner race 101. Then, balls 103 are inserted into the space 102 at widest portion thereof. After all the balls 103 have been inserted, the outer race 100 and the inner race 101 are made coaxial to each other. According to this assembly, the number of the balls to be inserted is limited. As a result, the load capacity of the ball bearing is limited. Further, it is necessary to hold the balls 103 by means of a retainer 104 or 104' as shown in FIG. 6a or FIG. 6b, both identified as Prior Art in order to prevent the balls from collecting to one part of the space 102 in the circumferential direction of the ball bearing.
For the purpose of increasing the load capacity of the ball bearing, it might be effective to use another type of ball bearing provided with a greater number of balls inserted in a space defined between an outer race and an inner race. Such a ball bearing is disclosed in Japanese Patent Publication SHO 60-252837. The ball bearing of the Publication SHO 60-252837 includes a drive disk coupled to a crankshaft and a flywheel rotatably supported by the drive disk via a ball bearing. The ball bearing includes an outer race, an inner race and a plurality of balls. The balls are arranged in the circumferentially extended space defined between the outer race and the inner race so that any two adjacent balls contact each other in the circumferential direction of the ball bearing.
However, there are some problems with the above-described conventional ball bearings.
With respect to the deep groove ball bearing, since the number of the balls is limited, a load to be born by each ball is great. As a result, the balls tend to be abraded in a relatively short period of time, and the life of the ball bearing is relatively short.
With respect to the ball bearing wherein two adjacent balls contact each other, since ball inlet grooves should be formed in the outer race and the inner race of the ball bearing so that the balls can be inserted into the space defined between the outer race and the inner race through the ball inlet grooves, ball guide grooves formed in the outer race and the inner race are discontinuous in the circumferential direction of the ball bearing. In the case of a torque variation absorbing device including a hysteresis mechanism, an axial force generated by a cone spring of the hysteresis mechanism continuously acts on the ball bearing. Therefore, the balls contacting the discontinuous portions of the ball guide grooves of the outer race and the inner race will be quickly abraded due to the axial force and, as a result, the life of the ball bearing is relatively short.